The use of digital, as opposed to analog signals, for television broadcasts and the transmission of other types of video and audio signals has been proposed as a way of allowing improved picture quality and more efficient use of spectral bandwidth over that currently possible using analog NTSC television signals.
The International Standards Organization has set a standard for video data compression for generating a compressed digital data stream that is expected to be used for digital television. This standard is referred to as the ISO MPEG (International Standards Organization--Moving Picture Experts Group) ("MPEG") standard. In accordance with the MPEG standard, video data is encoded using discrete cosine transform encoding and is arranged into variable length encoded data packets for transmission.
Generally, digital television signals can be either standard definition signals having a resolution approximately that of current NTSC television, or high definition television signals which have a resolution that is greater that of current NTSC television signals.
One version of the MPEG standard, MPEG-2, is described in the International Standards Organization--Moving Picture Experts Group, Recommendations H.222.0 and H.262, ISO/IEC 13818-1 and 13818-2, respectively, titled "Information Technology--Generic Coding Of Moving Pictures and Associated Audio" (hereinafter "the November 1994 ISO-MPEG Committee International Standards") hereby expressly incorporated by reference. Any references made in this patent application to MPEG video data is to be understood to refer to video data that complies with MPEG-2 standards as defined in the November 1994 ISO-MPEG Committee International Standards unless otherwise indicated.
Picture-in-picture capability has become a widely accepted and often desired feature of modern analog televisions. To meet anticipated demand for picture-in-picture capability in digital televisions, it will be necessary for a digital television, e.g., an MPEG-2 compatible television, to decode video data representing two pictures. The two pictures can then be displayed as a picture within a picture to achieve the desired picture-in-picture effect.
In known analog picture-in-picture systems, during picture-in-picture operation, a first full resolution decoder is normally used to decode the TV signal used to produce a main picture and a second full resolution decoder is used to decode the television signal which is used to provide the second, e.g., inset, picture displayed within a small area of the main picture. Thus, in current analog systems a complete additional tuner and decoder is normally used to provide picture-in-picture capability. The picture-in-picture capability featured by current analog televisions typically produces an inset picture whose size is approximately 1/4.times.1/4 to 1/3.times.1/3 of the full size display.
The cost of providing two full resolution digital video decoders and, in particular, the memory required to implement two such decoders, in the case of digital video signals is likely to be significant.
In order to achieve customer acceptance in home video systems, it is desirable that the cost associated with adding picture-in-picture capability to a digital television set be minimized.
Accordingly, there is a need for methods and apparatus that can be used to provide picture-in-picture capability in, e.g., video decoding and display devices such as digital television sets, at a minimal cost.